This invention relates to graphic imaging systems and more specifically character printers which are particularly useful in phototypesetters.
During the last 30 years, numerous so-called second generation phototypesetters have been marketed. These machines flash-illuminate characters positioned upon a whirling character disk or drum, and the resulting optical image is projected by a lens system upon a photosensitive film. The size of the characters are changed by means of moving zoom lenses or the like or by rotating a lens turret to position various lenses at the optical projection axis. The characters are sequentially recorded upon the photosensitive film by mechanically scanning such film which may be accomplished in various ways. The film carriage may be moved relative to the optical axis, the projection lenses may be moved relative to the film platen, the whirling character disk may be moved relative to the film platen, or various combinations of the foregoing may be employed to sequentially project the characters upon the film to form a line of characters. Generally, the projection lens carriage assemblies are relatively heavy and bulky, as is the drum or disk bearing the images of the characters to be projected. Also, changes in the fonts involve manual replacement of the character disks, or film strips mounted upon a drum. Additionally, the electromechanical stepping devices for producing the above mentioned scanning motions are also relatively bulky and cumbersome. The speed of second generation machines is limited by the output carriage escapement speed and by character access time determined by the rotational speed of the font disk.
So-called third generation phototypesetters were introduced in the 1960s, most of which utilize cathode ray tubes for generating the characters upon the face of the tube. These character images are thereafter optically projected upon the film. In contrast with the components of the second generation machines, the electron beam is inertialess and the binary character codes thus may actuate the beam at much higher speeds than those obtainable by the second generation machines. Inertialess laser generated light beams have also been employed rather than cathode ray tubes. Many font families may be generated by these machines since the character generating codes may be densely packed during recordation upon magnetic storage media, such as floppy disks. Also, the character size may be electronically changed by changing the length of the beam traces making up the character components (See FIG. 1 of U.S. Pat. No. 3,952,311).
The result of the foregoing is that these machines have higher speeds, and greater flexibility in the character shapes and sizes produced. However, the third generation machines are usually considerably more expensive than the second generation machines; in 1979, they typically sold for $40,000 on up. In contrast, second generation machines in 1979 have been marketed for around $10,000.
It is a principal object of the present invention to provide a fourth generation phototypesetter that can be marketed for around $10,000, and yet have the speed and flexibility of third generation machines.
It is a further object of the invention to provide a phototypesetter that is relatively light in weight and compact, since the relatively bulky high mass components of the second generation phototypesetters have been eliminated.
It is yet a further object of the present invention to provide a radically new phototypesetter having a printing device which is very inexpensive and may be rapidly replaced to reduce maintenance costs.
The use of arrays of fiber optic bundles for printing characters is old in the art. In U.S. Pat. No. 3,832,488, a matrix of light emitting diodes (LEDs) selectively illuminates the input ends of the fiber optic light pipes and a lens focuses the resulting image at the output of light pipes upon microfilm. In U.S. Pat. No. 3,988,742, a fiber optic bundle is in direct contact with microfilm and is controlled by binary signals which selectively operate an LED array. In U.S. Pat. No. 2,982,175, the input ends of the fiber optic bundle are illuminated in accordance with an optical image. In U.S. Pat. No. 4,000,495, an array of 5,000 fibers contact the film and record the characters thereon; see also U.S. Pat. Nos. 3,952,311, 3,458,655, and 3,644,922.
In U.S. Pat. No. 3,699,516, a two-dimensional optical image is projected by a lens turret upon the input end of a fiber optic cable, and means are provided for causing the output end of the cable to scan a photosensitive medium along with a lens which projects the image at the output of the cable upon the medium to set type. Since the optical image is two-dimensional, a linear array of filaments cannot be used, and thus, the fiber optic cable is relatively heavy. It is believed that in the commercial phototypesetting machine marketed by Graphic Systems, Inc., having the configuration of this patent, the fiber optic cable had over 300,000 fibers. As a result, the scanning speed was quite slow due to the high mass of the cable compared to the high scanning speed of the printing head of the present invention. This machine is also relatively heavy and bulky and cumbersome owing to the use of a font drum and lens turret.
In spite of the existence of the above-mentioned prior art, an inexpensive high-speed phototypesetter capable of setting over 500 newspaper lines per minute, for example, has never been marketed. It is believed that this has not occurred since the direct application of the teachings of the prior art would require thousands of fiber optic filaments, which is impractical due to the failure rate of the various components. Failures in the operation of the LEDs, failures in the joints between the LEDs and the input ends of the optical fibers, fiber breakage, and misalignment between the input ends of the fiber optic filaments and the LEDs all create substantial problems with respect to the application of LED illuminated fiber optic arrays.
For example, if one were to construct a phototypesetter following the teachings of Lapeyre, U.S. Pat. No. 3,952,311, 3,000 optical fibers would be required for a 10-inch line length since 300 emitters per inch are required (see lines 61 and 62 of Column 2 of this patent). It is also obvious from the inspection of James et al, U.S. Pat. No. 3,644,922, that thousands of fibers would be required. It may be demonstrated statistically that the reject rate in manufacturing increases at a rate which is nonlinear relative to the number of fibers, so that the use of a scanning head having relatively few fibers in the present invention, for the first time, renders this approach practicable.
If, for the purpose of comparison, one assumes that during manufacturing, a yield of 50% good fiberoptic/LED transducers can be achieved with 128 LED transducers, then one can calculate as follows, using well-recognized probability theory, that 3,000 LED transducers will have a virtually unusable yield of 0.0000088%.
assume: P.sub.128 =0.5 PA0 then: PA0 P.sub.128 =0.5=(P.sub.L).sup.128 and P.sub.3000 =(P.sub.L).sup.3000 PA0 therefore: ##EQU1## where: P.sub.128 =probability of a good transducer having 128 LEDs PA0 P.sub.3000 =probability of a good transducer having 3000 LEDs PA0 P.sub.L =probability of any one LED being good.
Thus, it is an important object of the invention to drastically reduce the number of fiber optic filaments which are employed, to alleviate the problem of the above stated failures. Should such failures occur, it is a further object of the invention to provide a printing device which is inexpensive and is readily replacable.
It is a further object of the invention to provide a novel print head drive carriage which is inexpensive to manufacture and which will maintain accurate tolerances in that no "play" will exist with respect to undesired slight random motion of the print head, and at the same time, the carriage drive will not be susceptible to jamming. It is a further object of the invention to provide a novel drive belt to print head carriage coupling arrangement which prevents belt misalignment from inducing undesirable random motion of the print head.